Color Notes - Tree Trunks

Brown tree trunks are not really brown in most cases.  They are actually very grey on the oaks in front of me.  I would use some Burnt Umber and add some white to get a grey color of brown with maybe a spec of black.  And then to deepen them in spots where the bark is cracked, I would mix some Burnt Umber and my good friend Cadmium Orange.  I noticed also that in front of me the trunks are lighter and get darker in the trees that are furthest from me.  This is not to say they are more vivid in color, just getting darker due to the leaf cover.  A lot of light is striking the trunks closest to me.